The present invention relates to the field of liquid crystal displays (LCD""s). Specifically, embodiments of the present invention relate to an LCD power loss indication.
Portable electronic devices, such as telephones, calculators, personal digital assistants, handheld computer systems or two-way radios are frequently equipped with LCD display screens. These devices are generally powered using either rechargeable or disposable batteries. There are many other similar types of electronic devices that have a battery and an LCD screen. Video game systems, pagers, GPS""s, watches, clocks, and other such devices are examples of other types of electronic devices in common use that may contain a battery and an LCD display screen.
Many of these devices have displays and/or alarms to apprise a user when the battery power is low. One conventional approach to apprising a user of low battery power is by use of a display that is illustrated in FIGS. 1A-1D. FIG. 1A illustrates an LCD display screen 100a showing a fully charged battery as exemplified by the image of a battery having three areas indicated to represent full power. FIG. 1B illustrates an LCD display screen 100b showing a partially charged battery as exemplified by the battery image having two areas indicated and one area appearing blank, signifying a lack of charge. Likewise, FIG. 1C illustrates an LCD screen 100c showing a low battery charge as exemplified by only one area indicated and the remaining area blank. FIG. 1D is an illustration of an LCD screen 100d that is inoperable, according to the prior art. The inoperability may be the result of a dead or missing battery, or it may be the result of a faulty device. If there is a dead battery or one that is not present, there is no electricity to light the indicator on the display or to sound an alarm. Thus, there is no apparent way to determine whether the screen is not showing a display because of a lack of power or because either the screen or the device containing the screen is broken.
FIG. 2A is an exploded diagram of a non-energized LCD display in accordance with prior art. The LCD is composed of a series of layers, beginning with a mirrored substrate 201 upon which is layered a continuous polarizing filter 202 with a specific orientation. Upon the polarizing filter is a semi-continuous electrode layer 203 that has spaces corresponding to the locations of connectors on electrode layer 207. Liquid crystal layer 205 is layered between alignment gratings 204 and 206, together with which, in a nonenergized state, it rotates the plane of polarization of light through a ninety degree angle as represented by arrow 210.
Referring still to FIG. 2A, discontinuous electrode layer 207 has electrodes in the contour of an image, such as shown in FIGS. 1A-1C, to be displayed when the LCD is energized. There are connectors running from the image to the edge of electrode layer 207 that are mimicked by the spaces in electrode layer 203 below so that they will not be displayed in an energized state. Above discontinuous electrode layer 207 is another continuous polarizing filter layer 208 that has a plane of polarization oriented at 90 degrees from that of continuous polarizing filter layer 202. Next is a layer of glass 209 at the top surface of the LCD display.
Light passing into the LCD display of FIG. 2A strikes the first polarizing filter 208 and is polarized. The polarized light then passes through the liquid crystal and alignment grating layers, where the molecules in the layers change the light""s plane of vibration to match their own angle. When the light reaches the far side of these layers, it has been rotated ninety degrees and is matched up with the continuous polarizing filter layer 202, so it will pass through and reflect off the mirrored surface of the substrate. The reflected light passes back up through the layer stack, is again rotated by the liquid crystal layer, and is able to pass through both polarizing layers, out of the display and into the eye of an observer, thus appearing transparent on the display.
FIG. 2B is an exploded diagram of an energized LCD display in accordance with prior art. In this case electrode layers 207 and 203 are energized and have common-plane energized electrodes in the contour of the image 212. The liquid crystal molecules untwist, as indicated by arrow 211, between the common plane of energized electrodes and the polarized light in that region is blocked by polarizing filter 202. This causes the LCD to display the image as a dark area on a bright background.
While the prior art displays a depletion of the battery charge and an approaching loss of power, when the power is completely depleted or missing, it shows no indication at all. Thus, a user does not know whether the battery is dead or missing, or whether the device is in some way defective.
A device and method for indicating a power loss in an LCD is disclosed. In one embodiment, the device provides a display that indicates an absence of power to the LCD. The device includes a continuous polarizing filter layer disposed within a display area that makes up a portion of the total display area of the LCD. A layer of liquid crystals is disposed between alignment gratings and coupled to the continuous polarizing filter layer. In one embodiment a discontinuous polarizing filter layer is optically coupled to the layer of liquid crystals. The discontinuous polarizing filter layer has a plane of polarization aligned with the plane of polarization of the continuous polarizing filter, and the discontinuous polarizing filter layer comprises a contour within the display area conforming to an image, wherein the image is displayed in the absence of an electric field.